In the field of fluid dynamics, the experiments of the wind tunnel and water tunnel are essential to design, analyze and research in flow machines. Based on such experiments, the variations of a flow around a test object in the flow field can be observed directly. Therefore, in order to visualize the flow field, an appropriate observing method is necessary. The most direct observing method is a visual observing method, i.e. an observing method via images.
Please refer to FIG. 1, which is a diagram showing an observing device and method for observing a flow field according to the prior art. In FIG. 1, the region surrounded by dotted lines indicates a flow field 3. Generally, no matter in a wind tunnel or a water tunnel experiment, when one skilled in the art wants to realize the flow dynamics at a specific position, particles will be dropped into the upstream of the specific position in the flow field. For example, for a stable flow field in a wind tunnel, smoke will be released therein, and for a water tunnel, a dye will be suspended therein. Meanwhile, the moving image of the particles are captured and recorded by a camera 1. In order to facilitate the observation, a light sheet 4 generated by a light sheet generator 2 for traversing the flow field 3 and thus generating a light sheet section 40 in the flow field 3 is provided in the prior art. Since the light axis of the camera 1 is perpendicular to the plane of the light sheet section 40, it is facile for the camera 1 to focus on each point on the light sheet section 40. Furthermore, since what is launch into the flow field 3 is a light sheet 4, the light sheet section 40 is illuminated particularly. Therefore, the particles (not shown) suspended in the light sheet section 40 will be illuminated and revealed, which are helpful to take images of the light sheet section 40 by the camera 1.
Please refer to FIG. 2, which is a diagram showing the actual operation of the observing device according to FIG. 1. A test object 30 configured in the flow field 3 is in a shape of a wing. When the light sheet crosses the flow field 3 and a light sheet section 40 is generated, a wing-shaped section 30′ is generated on the test object 30. Since the test object 30 is merely varied in the directions of X-axis and Y-axis of the plane of the wing-shaped section 30′ and constant in the direction of Z-axis thereof, only the variations in the directions of X-axis and Y-axis, i.e. the X-Y plane, are needed to be observed instead of in the direction of Z-axis. Accordingly, the light sheet section 40 crossing the flow field 3 is in a direction for capturing the image of the X-Y plane, and the flow in the flow field 3 passes through the test object 30 along a flowing direction 31. Under the condition that the flow field 3 is stable, pathlines 31′ representing the trajectory of particles released into the flow field 3 and varied by the flow could be observed, and thereby the variations of the flow passing through the test object 30 are realized.
However, in fact, the test object to be observed in the wind tunnel or the water tunnel usually varies in all the three directions. Supposing the test object 30 in FIG. 2 is varied in Z-direction as well, the flow will have a component in Z-direction when passing through the test object 30. However, for the conventional device in FIG. 1, even if the flow field 3 is maintained in stable, the flow phenomenon in Z-direction still cannot be visualized. Likewise, the respective flow phenomenons in two X-Y planes with different Z-values are hard to be distinguished therebetween by the visualization thereof, and thus an analysis for the two planes is hard to be made.
Accordingly, in order to establish a complete observing result of a three dimensional flow field, a whole new method and apparatus for taking images of the flow field are necessary, and the purpose thereof is to visualize a flow field on different planes nimbly, quickly and almost simultaneously.
Hence, because of the defects in the prior arts, the inventors provide an observing device and method to effectively overcome the demerits existing in the prior arts.